Patent Application
20250073634
The invention relates to an apparatus for separating carbon dioxide from gases, in particular from offgases.
In order to reduce man-made climate change, emission of carbon dioxide into the atmosphere is increasingly being avoided. Instead, attempts are made to separate carbon dioxide formed and then either convert it or send it for storage. A typical process to this end comprises scrubbing offgases with a basic solution, for example an amine solution, at about 25° C. to 50° C. This amine solution acts as a solvent in which the carbon dioxide dissolves. The solution containing the carbon dioxide is then heated and in a desorption step the carbon dioxide is converted back into the gas phase. This restores the solvent and also affords a pure carbon dioxide gas stream. The carbon dioxide gas stream may then, for example and purely exemplarily, be sent for storage or supplied to a methanol synthesis.
WO 2010/086 039 A1 discloses a process and an apparatus for separating carbon dioxide from an offgas of a fossil-fired power plant.
CN 111203086 A discloses a CO2 separation system with low energy consumption and low emissions.
WO 2014/077 919 A1 discloses an apparatus and a process for removing acidic gases from a gas stream and regeneration of the absorbent solution.
US 2017/0197175 A1 discloses an energy-efficient process for extracting acidic gases from a gas stream.
WO 2013/013 749 A1 discloses thermal recovery in absorption and desorption processes.
WO 2019/232 626 A1 discloses a CO2 separation after combustion with thermal recovery.
All plants for separating CO2 have in common that energy must be supplied for re-emission of the CO2 from the solution. To this end, heat at a high and thus comparatively valuable level is employed.
It is an object of the invention to provide a carbon dioxide separation apparatus where the overall process of absorption and desorption is energetically optimized.
This object is achieved by the carbon dioxide separation apparatus having the features specified in claim 1. Advantageous developments are apparent from the dependent claims, the following description and the drawings.
The carbon dioxide separation apparatus according to the invention comprises an absorption apparatus and a desorption apparatus. In the absorption apparatus the gas to be purified of carbon dioxide is introduced and the carbon dioxide from the gas phase transferred into the liquid phase through contact with a solvent, usually an amine solution. This forms a solution of the solvent with the carbon dioxide dissolved and optionally bound therein. This solution is transferred into the desorption apparatus where the carbon dioxide is re-expelled from the solution so that the solvent is recovered and recycled into the absorption apparatus. A carbon dioxide gas stream which may be sent for further use is likewise obtained. This basic principle is already used in numerous variations.
The absorption apparatus has a gas inlet for the gas to be purified and a gas outlet for the purified gas. The gas to be purified may be an offgas from the combustion of fossil fuels for example. The purified gas would then be mainly nitrogen with a small remainder of carbon dioxide and optionally a proportion of oxygen which is markedly reduced by the combustion process. The purified gas may then be emitted to the atmosphere for example without releasing large amounts of the greenhouse gas carbon dioxide. The absorption apparatus typically comprises one or more mass transfer elements arranged between the gas inlet and the absorption solvent inlet. The mass transfer elements serve to better contact the liquid phase and the gaseous phase, in particular also to increase the surface area of the liquid phase. Such mass transfer elements are known to those skilled in the art and may be for example bubble cap trays, random packings or a structured packing.
The absorption apparatus further comprises an absorption solvent inlet and a solution outlet. The absorption solvent inlet is typically arranged at the top of the absorption apparatus and the solution outlet at the bottom of the absorption apparatus. Accordingly the gas inlet is typically arranged at the bottom and the gas outlet at the top so that gas and solvent flow through the absorption apparatus in countercurrent.
The desorption apparatus comprises at least a first solution inlet, an absorption solvent outlet, a hot solvent inlet and a carbon dioxide outlet. The solution outlet of the absorption apparatus is connected to the first solution inlet of the desorption apparatus via a first solution conduit. The first solution conduit comprises a first heat exchanger. This heats the solvent stream flowing through the first solution conduit so that the carbon dioxide present in the solution can be re-emitted in the desorption apparatus. The absorption solvent outlet of the desorption apparatus is connected to the absorption solvent inlet of the absorption apparatus via an absorption solvent conduit. The solvent depleted of carbon dioxide in the desorption apparatus flows back to the absorption apparatus via the absorption solvent conduit. The absorption solvent conduit likewise comprises the first heat exchanger. This transfers the heat of the solvent stream in the absorption solvent conduit to the solution stream. The absorption solvent conduit comprises a branch to a hot solvent conduit. A substream of the solvent stream is thus diverted and passed into the hot solvent conduit. The hot solvent conduit is connected to the hot solvent inlet. The hot solvent conduit comprises a second heat exchanger. This allows additional energy to be introduced into the overall system. The desorption apparatus typically comprises one or more mass transfer elements arranged above and below the first solution inlet. The mass transfer elements serve to better contact the liquid phase and the gaseous phase, in particular also to increase the surface area of the liquid phase. Such mass transfer elements are known to those skilled in the art and may be for example bubble cap trays or random packings.
According to the invention the pressure of the solvent in the second heat exchanger is 0.2 bar to 5 bar higher than the pressure in the desorption apparatus at the absorption solvent outlet. A higher starting temperature can thus be achieved in the second heat exchanger since the elevated pressure increases the boiling point. This in turn has the result that the solvent has a higher temperature at the absorption solvent outlet and thus passes into the first heat exchanger at a higher temperature. This makes it possible for said exchanger to be made more compact or to attain a higher starting temperature for the laden solution stream from the first heat exchanger. The latter in turn leads to more efficient stripping of the carbon dioxide from the solution.
The pressure of the solvent in the second heat exchanger is adjustable within apparatus limits. There are two exemplary and preferred embodiments of specific adjustment of the pressure via the apparatus. In a first exemplary and preferred embodiment of the invention the pressure of the solvent in the second heat exchanger is 0.2 bar to 5 bar higher than the pressure in the desorption apparatus at the absorption solvent outlet because the second heat exchanger is arranged at least 1 m in height below the absorption solvent outlet so that the pressure in the second heat exchanger is increased by the hydrostatic column of the solvent corresponding to the total height difference. In a second exemplary and preferred embodiment of the invention the pressure of the solvent in the second heat exchanger is 0.2 bar to 5 bar higher than the pressure in the desorption apparatus at the absorption solvent outlet because a first pump for producing the corresponding positive pressure is arranged upstream of the second heat exchanger.
In a further embodiment of the invention a pressure reduction means, for example a control valve, an aperture plate or a pipe narrowing, is arranged between the second heat exchanger and the desorption apparatus. The pressure reduction means establishes/maintains the desired positive pressure in the second heat exchanger on the gas/vapor side. This can prevent evaporation in the second heat exchanger if necessary.
It is preferable when the first solution inlet is arranged in the middle region of the desorption apparatus.
In a further embodiment of the invention the first solution conduit comprises an evaporation apparatus downstream of the first heat exchanger. The evaporation apparatus, also known as a decompression vessel, ensures that the solution of the solution stream heated in the first heat exchanger can undergo decompression and partially evaporate. The liquid phase of the solution stream is thus separated from the gaseous phase of the solution stream in the evaporation apparatus. The liquid phase is passed into the desorption apparatus via the first solution conduit. Application of the liquid phase via the first solution conduit and the first solution inlet is preferably effected between two mass transfer elements. The desorption apparatus further comprises a vapor inlet and the evaporation apparatus comprises a vapor outlet. The vapor outlet of the evaporation apparatus and the vapor inlet of the desorption apparatus are connected to a gas solution conduit for transfer of the gaseous phase. It is particularly preferable when the vapor inlet is arranged in the lower region of the desorption apparatus. It is preferable when no mass transfer elements are arranged in the lower region. This optimizes the energetic management of the entire process.
In a further embodiment of the invention, a second solution conduit branches off from the first solution conduit between the absorption apparatus and the first heat exchanger. The second solution conduit leads directly into the top of the desorption apparatus. In this context directly is to be understood as meaning without a heat exchanger or the like. A (flow control) valve may optionally be arranged here. Thus the carbon dioxide-laden solution is itself used to cool the gas stream emerging from the desorption apparatus. This has the result that the heat supplied from the first heat exchanger and the second heat exchanger and that supplied to the desorption means remains in the desorption means and in the solvent and is not emitted to a cooling medium.
The carbon dioxide separation apparatus according to the invention is more particularly elucidated hereinbelow with reference to a exemplary embodiment shown in the drawings.
The illustrations shown are purely schematic and serve to illustrate the invention. The same parts of the different exemplary embodiments are given the same numbers for the sake of simplicity. 10
In the desorption apparatus 30 the carbon dioxide is thermally removed from the solution and discharged via the carbon dioxide outlet 34. This carbon dioxide stream may then be supplied for example to a further reaction or to storage. The solvent freed of carbon dioxide collects on the bottom of the desorption apparatus 30 and is supplied through the absorption outlet 32 to the absorption conduit 50. The solvent stream gives its thermal energy to the solution stream in the first heat exchanger 41. For example a fourth pump is used to pass the solvent stream via a third heat exchanger 55 through the absorption solvent inlet 23 into the absorption apparatus.
A substream is diverted from the solvent stream in the absorption solvent conduit 50 at the branch 51 and is conveyed through the hot solvent conduit 52 via the second heat exchanger 53 in particular in vaporous form or as a vapor/liquid mixture through the hot solvent inlet 33 back into the desorption apparatus 30. The required energy for stripping the carbon dioxide from the solution is supplied to the system via the second heat exchanger 53. The second heat exchanger 53 is arranged for example 3.5 m below the absorption solvent outlet 32 so that the water column establishes an overpressure of about 0.35 bar. This allows the second heat exchanger 53 to heat the solvent substream to a higher temperature which in turn has the result that the entry temperature of the solvent stream passed through the absorption solvent conduit 50 is also correspondingly elevated upstream of the first heat exchanger 41.
The second exemplary embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| BE 2021/6009 | Dec 2021 | BE | national |
| 10 2021 214 786.0 | Dec 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/086195 | 12/15/2022 | WO |
